Degradation of Three Microcystin Variants in the Presence of the Macrophyte Spirodela polyrhiza and the Associated Microbial Communities.

Cyanobacteria, which form water blooms all over the world, can produce a wide range of cyanotoxins such as hepatotoxic microcystins (MCs) and other biologically active metabolites harmful to living organisms, including humans. Microcystin biodegradation, particularly caused by bacteria, has been broadly documented; however, studies in this field focus mainly on strains isolated from natural aquatic environments. In this paper, the biodegradation of microcystin-RR (MC-RR), microcystin-LR (MC-LR), and microcystin-LF (MC-LF) after incubation with Spirodela polyrhiza and the associated microorganisms (which were cultured under laboratory conditions) is shown. The strongest MC biodegradation rate after nine days of incubation was observed for MC-RR, followed by MC-LR. No statistically significant decrease in the concentration of MC-LF was noted. Products of MC decomposition were detected via the HPLC method, and their highest number was found for MC-RR (six products with the retention time between 5.6 and 16.2 min), followed by MC-LR (two products with the retention time between 19.3 and 20.2 min). Although the decrease in MC-LF concentration was not significant, four MC-LF degradation products were detected with the retention time between 28.9 and 33.0 min. The results showed that MC-LF was the most stable and resistant MC variant under experimental conditions. No accumulation of MCs or their biodegradation products in S. polyrhiza was found. The findings suggest that the microorganisms (bacteria and algae) associated with S. polyrhiza could be responsible for the MC biodegradation observed. Therefore, there is a need to broaden the research on the biodegradation products detected and potential MC-degraders associated with plants.

Long-term responses of epiphytic midges (Diptera, Chironomidae) to emergent macrophytes removal and P concentrations in a shallow hypertrophic lake ecosystem.

Chironomid larvae are used as indicators of environmental changes in neolimnological and paleolimnological research. In the present study, we evaluated the responses of epiphytic chironomids to changes in environmental conditions over a long time scale. We intended to decipher whether changes in the trophic status of a lake (hypertrophic-eutrophic) would affect the taxonomic structure of epiphytic chironomids by influencing their food availability (structure of periphytic algae) and whether the responses of chironomids are taxa specific. In a shallow hypertrophic lake ecosystem, epiphytic chironomids associated with the emergent macrophyte Phragmites australis were studied from 2001 to 2018. In the autumn of 2006, emergent macrophyte removal led to an improved water transparency and reduced phytoplankton biomass. Epiphytic chironomids responded clearly to the shift from hypertrophic to eutrophic conditions. Under hypertrophic conditions larvae of detritivorous Cricotopus sp. (gr. sylvestris) and filter-feeder larvae of Glyptotendipes sp. prevailed. After macrophyte removal, we observed high relative abundances of Endochironomus albipennis and Paratanytarsus austriacus, which are classified as grazers, utilise periphytic algae (mainly diatoms) as a food source. The results indicated that the density of P. australis, relative abundances of cyanobacteria and diatoms in periphyton communities, Secchi disc depth, and periphytic and planktonic Chl-a are significant determinants of the diversity of epiphytic chironomids. The results can provide a reliable reference to the neolimnological and paleominological studies on chironomid responses to multiple environmental stressors in shallow lakes.

Environmental implications of potamophases duration and concentration period in the floodplain lakes of the Bug River valley.

The Bug River, in the section between Dorohusk and Wlodawa (part of the eastern UE border), is one of the last remaining natural rivers in Europe. Thus, its abundance of floodplain lakes (FPL) in that part constitutes an area which preserves biodiversity. This study presents an analysis of potamophases duration and the Potamophases Concentration Index (PCI) in 20 floodplain lakes in the multi-year period 1952-2014. One-way analysis of variance (ANOVA, Tukey test), as well as a correlogram approach were used to perform statistical analyses. Among the lakes, few differed significantly from the others; more often, differences between years, in terms of both potamophase duration and PCI, were found. This proved that time is more important than space in shaping river valley hydrology. Cumulative values of the study indices, presented in a correlogram, showed that both potamophase duration and the period of potamophase concentration determine the water quality of a floodplain lake, expressed as the hydro-chemical type. In floodplain lakes with short potamophases concentrated at the beginning of a hydrologic year, water quality typical for interzonal lakes was observed; in floodplain lakes with the longest potamophases with their concentration at the end of a hydrologic year, ionic concentrations typical of extrazonal lakes occurred, whereas in lakes with a potamophase duration close to the average value and a spring concentration of floods, intermediate water quality was observed, typical of mixozonal lakes. A sound knowledge of floodplain lake functioning is crucial to maintaining the biodiversity of river valleys due to the lake's natural water and nutrient storage capacity.

The Effects of Cyanobacterial Bloom Extracts on the Biomass, Chl-a, MC and Other Oligopeptides Contents in a Natural Planktothrix agardhii Population.

Blooms of the cyanobacterium Planktothrix agardhii are common in shallow, eutrophic freshwaters. P. agardhii may produce hepatotoxic microcystins (MCs) and many other bioactive secondary metabolites belonging mostly to non-ribosomal oligopeptides. The aim of this work was to study the effects of two extracts (Pa-A and Pa-B) of P. agardhii-predominated bloom samples with different oligopeptide profiles and high concentration of biogenic compounds on another natural P. agardhii population. We hypothesised that the P. agardhii biomass and content of oligopeptides in P. agardhii is shaped in a different manner by diverse mixtures of metabolites of different P. agardhii-dominated cyanobacterial assemblages. For this purpose, the biomass, chlorophyll a and oligopeptides content in the treated P. agardhii were measured. Seven-day microcosm experiments with four concentrations of the extracts Pa-A and Pa-B were carried out. Generally, aeruginosins (AERs), cyanopeptolins (CPs) and anabaenopeptins (APs) were the most numerous peptides; however, only 16% of them were common for both extracts. The addition of the extracts resulted in similar effects on P. agardhii: an increase in biomass, Chl-a and MC content in the exposed P. agardhii as well as changes in its oligopeptide profile were observed. MCs present in the extracts did not inhibit accumulation of P. agardhii biomass, and did not have any negative effect on MC and Chl-a content. No evidence for bioaccumulation of dissolved peptides in the P. agardhii exposed was found. As the two tested extracts differed considerably in oligopeptide composition, but contained similar high concentrations of nutrients, it seems that biogenic compounds, not oligopeptides themselves, positively influenced the mixed natural P. agardhii population.

Effects of secondary metabolites produced by different cyanobacterial populations on the freshwater zooplankters Brachionus calyciflorus and Daphnia pulex.

Cyanobacterial blooms in eutrophic water bodies are a worldwide problem. Combined effects of mixtures of secondary metabolites produced by different cyanobacterial species on aquatic fauna are still not well recognised. We compared the survivorship of Brachionus calyciflorus Pallas (Rotifera) and Daphnia pulex Leyding (Cladocera) exposed to pure microcystin LR (MC-LR), anatoxin-a (ANTX) and to five extracts obtained from bloom-forming cyanobacteria Microcystis, Planktothrix and Dolichospermum. The obtained results revealed different response of the organisms to high concentrations of pure MC-LR, ANTX and complex cyanobacterial extracts. The extracts' toxicity to invertebrates was higher than that exerted by pure cyanotoxins and was dependent on the composition of cyanobacterial metabolites: Microcystis spp. extract containing anabaenopeptins A and B, aeruginosamide, four variants of cyanopeptolins and five MCs was not toxic to either of the organisms, whereas Planktothrix agardhii extract (I), containing anabaenopeptins A, B, F, 915, oscillamide Y, five different aeruginosins and four variants of MC was more toxic to daphnids than to rotifers. The extracts of another P. agarhdii (II) biomass and two different biomass samples of Dolichospermum spp. also affected survivorship of the rotifer and cladoceran, however, to various extent. It strongly suggests that non-ribosomal oligopeptides, other than MCs, had essential contribution to the observed toxicity to invertebrates and their effects on particular species or populations can vary depending on the secondary metabolite profiles of cyanobacteria.

Instability of Water Quality of a Shallow, Polymictic, Flow-Through Lake.

This paper describes catchment processes that favor the trophic instability of a shallow polymictic lake, in which a shift from eutrophy to hypertrophy occurs rapidly. In the lake, in 2007, the winter discharge maximum and an intensive precipitation (monthly sums exceeded 60 mm) in a vegetation season were observed. In 2007, the cyanobacterial blooms disappeared and the water trophy decreased. Total phosphorus (TP) was the main factor determining the high trophic status of the lake. The TP retention resulted from a quick flow of two inflows: QI1 (r = 0.64) and QI2 (0.56), and the base flow of tributary 1 (0.62). A significant negative correlation between TP and precipitation (r = - 0.54) was observed. Both the surface and the groundwater inflow of I4 showed a positive correlation with the retention of PO4 (r = 0.67 and r = 0.60, respectively), whereas the outlet discharge determined RNO3 (r = 0.57). The trophy of Lake Syczynskie was determined by the relationship between nutrient input and export, expressed as the ionic retention, Carlson's trophic state index (TSI), and phytoplankton abundance. The results showed that many factors influence the stability of water quality in small, polymictic lakes. However, in the studied lake, intense precipitation and winter discharge maxima (particularly base flow) prevented summer cyanobacterial blooms.

The biodegradation of microcystins in temperate freshwater bodies with previous cyanobacterial history.

Cyanobacterial blooms and cyanotoxins occur in freshwater lakes and reservoirs all over the world. Bacterial degradation of microcystins (MC), hepatotoxins produced by several cyanobacterial species, has also been broadly documented. However, information regarding MC biodegradation in European water bodies is very limited. In this paper, the occurrence and identification of MC biodegradation products was documented for 21 European lakes and reservoirs, many of which have well-documented cyanobacterial bloom histories. Varying cyanobacterial abundance and taxonomical composition were documented and MC producers were found in all the analysed samples. Planktothrix agardhii was the most common cyanobacterial species and it formed mass occurrences in four lakes. MC biodegradation was observed in 86% of the samples (18 out of 21), and four products of dmMC-LR decomposition were detected by HPLC and LC-MS methods. The two main products were cyclic dmMC-LR with modifications in the Arg-Asp-Leu region; additionally one product was recognized as the tetrapeptide Adda-Glu-Mdha-Ala. The composition of the detected products suggested a new biochemical pathway of MC degradation. The results confirmed the hypothesis that microcystin biodegradation is a common phenomenon in central European waters and that it may occur by a mechanism which is different from the one previously reported. Such a finding implies the necessity to develop a more accurate methodology for screening bacteria with MC biodegradation ability. Furthermore, it warrants new basic and applied studies on the characterization and utilization of new MC-degrading strains and biodegradation pathways.

Mass Development of Diazotrophic Cyanobacteria (Nostocales) and Production of Neurotoxic Anatoxin-a in a Planktothrix (Oscillatoriales) Dominated Temperate Lake.

In spite of extensive studies on multispecies toxigenic cyanobacterial blooms, they are still difficult to eliminate, and factors regulating their succession and toxin production remain still to discover. A 4-year study revealed periodical mass development of diazotrophic Nostocales such as Dolichospermum spp. (previously Anabaena), Aphanizomenon gracile and expansive Cuspidothrix (previously Aphanizomenon) issatschenkoi in a lake affected by perennial blooms of Planktothrix agardhii (Oscillatoriales). Compared to Oscillatoriales, Nostocales reached the highest total biomass (up to 16 mg L-1) and contributed nearly 33-85 % to the total biomass of filamentous cyanobacteria at higher water temperatures (average values 17.5-22.6 °C) and higher ratio (11.8-14.1) of dissolved inorganic nitrogen to dissolved inorganic phosphorus (DIN/DIP). Species structure of Nostocales changed considerably from year to year as indicated by the Jaccard similarity index (0.33-0.78). Concentrations of intracellular anatoxin-a (ANTX) ranged from 0.03 to 2.19 µg L-1 of the lake water, whilst extracellular toxin reached up to 0.55 µg L-1. The highest positive correlations were found between the intracellular ANTX and the biomass of Dolichospermum spp. (R2 = 0.73) and C. issatschenkoi (R2 = 0.43-0.65). Our study suggests that ANTX production by Dolichospermum depended mainly on water temperature, whereas that by C. issatschenkoi was related to water conductivity and DIN/DIP ratio. P-PO4 concentrations also seemed to be important. The relatively short-term mass development of neurotoxic Nostocales is an additional threat to shallow, highly eutrophic water bodies continuously affected by Oscillatoriales blooms and may be controlled mainly by the DIN/DIP ratio. ANTX should be considered as a pollutant of freshwaters.

Hydrochemical versus biological conditions of the functioning of three shallow lakes in Leczna-Wlodawa.

Lake-catchment relationships were presented with reference to each part of the subsystem. Ionic loads reflected the potential of the catchment areas and displayed the following pattern: Lake Rotcze < Lake Sumin < Lake Syczynskie; with respect to every ion, except nitrogen. The highest specific load of ions in Lake Syczynskie and the strong hydrochemical influence of the lake inlets facilitated the growth of water blooms of cyanobacteria, with a dominance of toxic filamentous P agardhii. It resulted in a poor ecological status of the lake (Q index = 0.8) and its hypertrophy (TSIchl-a = 78). The specific load of ions in the Lake Rotcze catchment (0.23 kg/yr-km(2) of P-PO4) contributed to the good ecological status (Q = 3.2) and mesotrophic character (TSIchl.a = 50) of the lake. Lake Sumin has a moderate catchment influence (2.41 kg/yr-km(2) of P-PO4), which facilitated moderate ecological (Q = 2.1) and trophic (eutrophy; TSIchlSa = 63) status.